U.S. patent application number 11/495241 was filed with the patent office on 2008-01-31 for fluid ejection devices and methods of fabrication.
Invention is credited to Bradley D. Chung, Jeremy Harlan Donaldson, Michael Hager, Thomas R. Strand.
Application Number | 20080024574 11/495241 |
Document ID | / |
Family ID | 38740355 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080024574 |
Kind Code |
A1 |
Donaldson; Jeremy Harlan ;
et al. |
January 31, 2008 |
Fluid ejection devices and methods of fabrication
Abstract
A fluid ejection device includes a fluidic layer assembly
mounted to a substrate, the fluidic layer assembly having a raised
portion formed on a side that faces away from the substrate. A
first nozzle is formed through a portion of the fluidic layer
assembly other than the raised portion, and a second, larger nozzle
is formed through the raised portion. A method of fabricating a
fluid ejection device includes applying a first layer of a
photoresist material to a substrate and a second layer of a
photoresist material to the first layer. A sequence of exposures
defines a first region of soluble material in the first layer that
becomes the first nozzle and second and third regions of soluble
material in the first and second layers, respectively, that jointly
become the second nozzle. A region of insoluble material in the
second layer becomes the raised portion.
Inventors: |
Donaldson; Jeremy Harlan;
(Corvallis, OR) ; Hager; Michael; (Corvallis,
OR) ; Chung; Bradley D.; (Coravallis, OR) ;
Strand; Thomas R.; (Corvallis, OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD, INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
38740355 |
Appl. No.: |
11/495241 |
Filed: |
July 28, 2006 |
Current U.S.
Class: |
347/88 |
Current CPC
Class: |
B41J 2/1634 20130101;
B41J 2/1629 20130101; B41J 2/1603 20130101; B41J 2/1628 20130101;
B41J 2/1631 20130101; B41J 2002/14475 20130101 |
Class at
Publication: |
347/88 |
International
Class: |
B41J 2/175 20060101
B41J002/175 |
Claims
1. A fluid ejection device comprising: a substrate; a fluidic layer
assembly mounted to said substrate, said fluidic layer assembly
having a first side facing said substrate and a second side facing
away from said substrate, and wherein said fluidic layer assembly
includes a raised portion formed on said second side; a first
nozzle formed through said fluidic layer assembly in a portion
other than said raised portion; and a second nozzle formed through
said fluidic layer assembly in said raised portion, wherein said
second nozzle has a larger cross-sectional area than said first
nozzle.
2. The fluid ejection device of claim 1 wherein said second nozzle
is longer than said first nozzle.
3. The fluid ejection device of claim 1 further comprising a first
fluid ejector associated with said first nozzle and a second fluid
ejector associated with said second nozzle.
4. The fluid ejection device of claim 1 wherein said fluid ejection
device is an inkjet printhead.
5. An inkjet printhead comprising: a substrate; a chamber layer
disposed on said substrate, said chamber layer defining first and
second firing chambers; a first bore layer disposed on said chamber
layer; a second bore layer covering a portion of said first bore
layer; a low drop weight nozzle formed through said first bore
layer so as to be in fluid communication with said first firing
chamber; and a high drop weight nozzle formed through said first
and second bore layers so as to be in fluid communication with said
second firing chamber, wherein said high drop weight nozzle has a
larger cross-sectional area than said low drop weight nozzle.
6. The inkjet printhead of claim 5 further comprising an ink feed
hole formed in said substrate, and wherein said low drop weight
nozzle is on one side of said ink feed hole and said high drop
weight nozzle is on another side of said ink feed hole.
7. The inkjet printhead of claim 5 wherein said low drop weight
nozzle is one of a plurality of low drop weight nozzles formed
through said first bore layer and said high drop weight nozzle is
one of a plurality of high drop weight nozzles formed through said
first and second bore layers.
8. The inkjet printhead of claim 7 further comprising an ink feed
hole formed in said substrate, and wherein said plurality of low
drop weight nozzles is located on one side of said ink feed hole
and said plurality of high drop weight nozzles is located on
another side of said ink feed hole.
9. A method of fabricating a fluid ejection device, said method
comprising: applying a first layer of a photoresist material to a
substrate; exposing portions of said first layer to electromagnetic
radiation to define first and second regions of soluble material in
said first layer, wherein said first region of soluble material is
smaller than said second region of soluble material; applying a
second layer of a photoresist material to said first layer;
exposing portions of said second layer to electromagnetic radiation
to define a third region of soluble material and a region of
insoluble material surrounding said third region of soluble
material, wherein said third region of soluble material is aligned
with said second region of soluble material; and removing soluble
material such that said first region of soluble material defines a
first nozzle, said second and third regions of soluble material
jointly define a second nozzle, and said region of insoluble
material defines a raised portion.
10. The method of claim 9 wherein exposing said first layer
includes a first exposure that defines said first region of soluble
material and a second exposure that defines said second region of
soluble material.
12. The method of claim 11 wherein said first exposure is performed
with a focus offset that produces a convergent profile for said
first region of soluble material and said second exposure is
performed with a focus offset that produces a divergent profile for
said second region of soluble material.
13. The method of claim 12 wherein exposing said second layer
includes an exposure performed with a focus offset that produces a
convergent profile for said third region of soluble material.
14. The method of claim 9 wherein said first layer is exposed prior
to applying said second layer to said first layer.
15. The method of claim 9 wherein a first portion of said first
layer is exposed prior to applying said second layer to said first
layer and a second portion of said first layer is exposed after
applying said second layer to said first layer.
16. The method of claim 15 wherein said second portion of said
first layer and portions of said second layer are exposed
together.
17. A fluid ejection device fabricated by the method of claim
9.
18. A method of fabricating an inkjet printhead, said method
comprising: providing a substrate; forming a chamber layer on said
substrate, said chamber layer defining firing chambers and feed
channels; and forming an fluidic layer assembly on said chamber
layer, said fluidic layer assembly having a step, low drop weight
nozzles, and high drop weight nozzles formed in said step.
19. The method of claim 18 wherein forming said fluidic layer
assembly includes: applying a first bore layer to said chamber
layer; applying a second bore layer to said first bore layer;
forming said low drop weight nozzles through said first bore layer
only; and forming said high drop weight nozzles through said first
and second bore layers.
Description
BACKGROUND OF THE INVENTION
[0001] Inkjet printing technology is used in many commercial
products such as computer printers, graphics plotters, copiers, and
facsimile machines. One type of inkjet printing, known as "drop on
demand," employs one or more inkjet pens that eject drops of ink
onto a print medium such as a sheet of paper. Printing fluids other
than ink, such as preconditioners and fixers, can also be utilized.
The pen or pens are typically mounted to a movable carriage that
traverses back-and-forth across the print medium. As the pens are
moved repeatedly across the print medium, they are activated under
command of a controller to eject drops of printing fluid at
appropriate times. With proper selection and timing of the drops,
the desired pattern is obtained on the print medium.
[0002] An inkjet pen generally includes at least one fluid ejection
device, commonly referred to as a printhead, which has a plurality
of orifices or nozzles through which the drops of printing fluid
are ejected. Adjacent to each nozzle is a firing chamber that
contains the printing fluid to be ejected through the nozzle.
Ejection of a fluid drop through a nozzle may be accomplished using
any suitable ejection mechanism, such as thermal bubble or
piezoelectric pressure wave to name a few. Printing fluid is
delivered to the firing chambers from a fluid supply to refill the
chamber after each ejection.
[0003] To increase print quality and functionality, it is desirable
to be able to eject printing fluid of different drop weights from a
single printhead. This can be accomplished by designing some of the
nozzles in a printhead to eject lower weight drops and other
nozzles to eject higher weight drops. However, the different
configurations used for the low drop weight nozzles and the high
drop weight nozzles make it difficult to optimize overall nozzle
performance. For example, the ability to provide adequate refill
speeds for the high drop weight nozzles can be compromised by the
ability to generate sufficient drop velocity for the low drop
weight nozzles, and vice versa. Accordingly, dual drop weight range
on a single printhead die is limited by an inherent tradeoff
between refill speed and drop velocity.
DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a perspective view of an inkjet pen.
[0005] FIG. 2 is a perspective view of an inkjet printhead.
[0006] FIG. 3 is a cross-sectional view of the printhead taken
along line 3-3 of FIG. 2.
[0007] FIGS. 4-8 are cross-sectional views illustrating the steps
of a first embodiment of fabricating a printhead.
[0008] FIGS. 9-11 are cross-sectional views illustrating the steps
of a second embodiment of fabricating a printhead.
[0009] FIGS. 12 and 13 are cross-sectional views illustrating the
steps of a third embodiment of fabricating a printhead.
DETAILED DESCRIPTION OF THE INVENTION
[0010] Representative embodiments of the present invention include
a fluid ejection device in the form of a printhead used in inkjet
printing. However, it should be noted that the present invention is
not limited to inkjet printheads and can be embodied in other fluid
ejection devices used in a wide range of applications.
[0011] Referring to the drawings wherein identical reference
numerals denote the same elements throughout the various views,
FIG. 1 shows an illustrative inkjet pen 10 having a printhead 12.
The pen 10 includes a body 14 that generally contains a printing
fluid supply. As used herein, the term "printing fluid" refers to
any fluid used in a printing process, including but not limited to
inks, preconditioners, fixers, etc. The printing fluid supply can
comprise a fluid reservoir wholly contained within the pen body 14
or, alternatively, can comprise a chamber inside the pen body 14
that is fluidly coupled to one or more off-axis fluid reservoirs
(not shown). The printhead 12 is mounted on an outer surface of the
pen body 14 in fluid communication with the printing fluid supply.
The printhead 12 ejects drops of printing fluid through a plurality
of nozzles 16 formed therein. Although only a relatively small
number of nozzles 16 is shown in FIG. 1, the printhead 12 may have
two or more columns with more than one hundred nozzles per column,
as is common in the printhead art. Appropriate electrical
connectors 18 (such as a tape automated bonding, "flex tape") are
provided for transmitting signals to and from the printhead 12.
[0012] Referring to FIGS. 2 and 3, the printhead 12 includes a
substrate 20, a thin film stack 22 disposed on top of the substrate
20, and a fluidic layer assembly 24 disposed on top of the thin
film stack 22. At least one ink feed hole 26 is formed in the
substrate 20, and the nozzles 16 are arranged around the ink feed
hole 26. The nozzles 16 are formed in the fluidic layer assembly 24
and comprise a group of low drop weight nozzles 16a and a group of
high drop weight nozzles 16b. In the illustrated embodiment, the
low drop weight nozzles 16a are arranged in a first column on a
first side of the ink feed hole 26 (the left side in FIG. 3), and
the high drop weight nozzles 16b are arranged in a second column on
a second side of the ink feed hole 26 (the right side in FIG.
3).
[0013] Associated with each nozzle 16a, 16b is a firing chamber 28,
a feed channel 30 establishing fluid communication between the ink
feed hole 26 and the firing chamber 28, and a fluid ejector 32
which functions to eject drops of printing fluid through the nozzle
16a, 16b. In the illustrated embodiment, the fluid ejectors 32 are
resistors or similar heating elements. It should be noted that
while thermally active resistors are described here by way of
example only, the present invention could include other types of
fluid ejectors such as piezoelectric actuators. The nozzles 16a,
16b, the firing chambers 28, the feed channels 30 and the ink feed
hole 26 are formed in the fluidic layer assembly 24, which is
fabricated as multiple layers (as described below). The resistors
32 are contained within the thin film stack 22 that is disposed on
top of the substrate 20. As is known in the art, the thin film
stack 22 can generally include an oxide layer, an electrically
conductive layer, a resistive layer, a passivation layer, and a
cavitation layer or sub-combinations thereof. Although FIGS. 2 and
3 depict one common printhead configuration, namely, two rows of
nozzles about a common ink feed hole, other configurations may also
be formed in the practice of the present invention.
[0014] The fluidic layer assembly 24 has a first side 34 that faces
the substrate 20 and a second side 36 that faces away from the
substrate 20. In the illustrated embodiment, the second side 36 is
non-planar or stepped. In this case, the fluidic layer assembly 24
includes a step or raised portion 38 formed on the second side 36,
such that the fluidic layer assembly 24 comprises the raised
portion 38, which is relatively thick, and a thinner base portion
40.
[0015] The low drop weight nozzles 16a are formed in the base
portion 40, and the high drop weight nozzles 16b are formed in the
raised portion 38. The high drop weight nozzles 16b have larger
cross-sectional areas than the low drop weight nozzles 16a to
provide larger drop weights. Furthermore, because the raised
portion 38 is thicker than the base portion 40, the high drop
weight nozzles 16b are longer or deeper than the low drop weight
nozzles 16a. As shown in FIG. 3, the nozzles 16a, 16b have a
substantially vertical bore profile. That is, the walls of the
nozzle bores are substantially perpendicular to the first and
second sides 34 and 36. The nozzles 16a, 16b can alternatively have
a tapered bore profile. If the nozzles have tapered bore profile,
this will preferably be in the form of a convergent taper in which
the nozzle opening is larger on the first side 34 than the second
side 36.
[0016] To eject a droplet from one of the nozzles 16a, 16b,
printing fluid is introduced into the associated firing chamber 28
from the ink feed hole 26 (which is in fluid communication with the
printing fluid supply (not shown)) via the associated channel 30.
The associated resistor 32 is activated with a pulse of electrical
current. The resulting heat from the resistor 32 is sufficient to
form a vapor bubble in the firing chamber 28, thereby forcing a
droplet through the nozzle 16a, 16b. The firing chamber 28 is
refilled after each droplet ejection with printing fluid from the
ink feed hole 26 via the feed channel 30.
[0017] By virtue of being longer and having a larger
cross-sectional area, the high drop weight nozzles 16b are able to
eject larger droplets without compromising refill speed or drop
velocity. Similarly, the low drop weight nozzles 16a can eject
smaller droplets without sacrificing refill speed or drop velocity
because they are shorter and have a smaller cross-sectional area.
Accordingly, the printhead 12 provides excellent dual drop weight
range on a single printhead die.
[0018] Referring to FIGS. 4-8, one process for fabricating an
inkjet printhead 12 is described. The process starts with a
substrate 20, which is typically a single crystalline or
polycrystalline silicon wafer. Other possible substrate materials
include gallium arsenide, glass, silica, ceramics, or a
semiconducting material. The substrate 20 has a first planar
surface 42 and a second planar surface 44, opposite the first
surface. The thin film stack 22 is formed or deposited on the first
surface 42 of the substrate 20 in any suitable manner, many such
techniques being well known in the art. As mentioned above, the
thin film stack 22 contains the fluid ejectors 32 and typically
includes some or all of an oxide layer, an electrically conductive
layer, a resistive layer, a passivation layer, and a cavitation
layer.
[0019] Next, the fluidic layer assembly 24, which will ultimately
define the nozzles 16a, 16b, the firing chambers 28 and the feed
channels 30, is formed on top of the thin film stack 22. In the
embodiment of FIGS. 4-8, the fluidic layer assembly 24 is
fabricated in three layers: a chamber layer, a first bore layer and
a second bore layer. These three layers are formed of any suitable
photoimagable materials. One such suitable material is a
photopolymerizable epoxy resin known generally in the trade as SU8,
which is available from several sources including MicroChem
Corporation of Newton, Mass. SU8 is a negative photoresist
material, meaning the material is normally soluble in developing
solution but becomes insoluble in developing solutions after
exposure to electromagnetic radiation, such as ultraviolet
radiation. All three layers can be made from the same material, or
one or more of the layers can be made of different photoimagable
materials. By way of example, this embodiment is described with all
three layers comprising a negative photoresist material. However,
it should be noted that positive photoresists could alternatively
be used. In this case, the mask patterns used in the photoimaging
steps would be reversed.
[0020] Fabrication of the fluidic layer assembly 24 begins by
applying a layer of a photoresist material to a desired depth over
the thin film stack 22 to provide a chamber layer 46, as shown in
FIG. 4. The chamber layer 46 is then imaged by exposing selected
portions to electromagnetic radiation through a first mask 48,
which masks the areas of the chamber layer 46 that are to be
subsequently removed and does not mask the areas that are to
remain. Because the chamber layer 46 is a negative photoresist
material (by way of example), the portions subjected to radiation
undergo polymeric cross-linking, which is depicted in the drawings
with double hatching, and become insoluble. In the illustrated
embodiment, the area of the chamber layer 46 that will be removed
is an area in the center of the chamber layer 46 that corresponds
to the firing chambers 28 and the feed channels 30.
[0021] After the light exposure, the chamber layer 46 is developed
to remove the unexposed chamber layer material and leave the
exposed, cross-linked material. This creates a developed area or
void 50, as seen in FIG. 5. The void 50 resulting from the removed
chamber layer material will eventually form the firing chambers 28
and the feed channels 30. The chamber layer 46 can be developed
using any suitable developing technique which includes, for
example, using an appropriate agent or developing solution such as
propylene glycol monomethyl ether acetate (PGMEA) or ethyl
lactate.
[0022] Referring to FIG. 6, a sacrificial fill material 52 is
applied so as to fill the void 50. The fill material 52 is then
planarized, such as through a resist etch back (REB) process or a
chemical mechanical polishing (CMP) process. This planarization
process removes any excess fill material to bring the fill material
52 in the void 50 flush with the upper surface of the chamber layer
46. Next, another layer of a photoresist material is applied to a
desired depth on the upper surface of the chamber layer 46 to
provide a first bore layer 54. The fill material 52 keeps first
bore layer material out of the void 50. The first bore layer 54 is
possibly, although not necessarily, made of the same material as
the chamber layer 46.
[0023] The first bore layer 54 is then imaged by exposing selected
portions to electromagnetic radiation through a second mask 56,
which masks the areas of the first bore layer 54 that are to be
subsequently removed and does not mask the areas that are to
remain. The areas of the first bore layer 54 that are to be removed
are a series of relatively small regions of unexposed, soluble
material that will become the nozzles 16a, 16b. In the illustrated
embodiment, this comprises a series of first regions 58a (only one
shown in FIG. 6) that will become the low drop weight nozzles 16a
and a series of second regions 58a (only one shown in FIG. 6) that
will become a lower portion of the high drop weight nozzles 16b.
The first and second regions 58a, 58b are aligned with
corresponding fluid ejectors 32. The second mask 56 can be
patterned such that the first regions 58a will be smaller in
cross-sectional area than the second regions 58b, so that the high
drop weight nozzles 16b will have larger cross-sectional areas than
the low drop weight nozzles 16a. For example, the first regions 58a
can be sized to be 13 microns in diameter, while the second regions
58b can be sized to be 20 microns in diameter.
[0024] The exposure is carried out at a predetermined focus offset
(i.e., the difference between the nominal focal length of the
photoimaging system and the relative positioning of the wafer) that
provides a desired profile for the regions 58a, 58b and thus a
desired bore profile for the nozzles 16a, 16b. In the illustrated
example, exposure is performed at a relatively high focus offset
(e.g., about 7-15 microns) to provide a convergent profile. The
first bore layer 54 is typically not developed at this point in the
process.
[0025] Turning to FIG. 7, another layer of photoresist material is
applied to a desired depth on top of the first bore layer 54 to
provide a second bore layer 60. The second bore layer 60 is
possibly, although not necessarily, made of the same material as
the chamber layer 46 and/or the first bore layer 54. The second
bore layer 60 is then imaged by exposing selected portions to
electromagnetic radiation through a third mask 62, which masks the
areas of the second bore layer 60 that are to be removed and does
not mask the areas that are to remain. The areas of the second bore
layer 60 that are to be removed include a series of third regions
of unexposed, soluble material 58c, wherein each third region 58c
is aligned with, and located above, a corresponding one of the
second regions 58b in the first bore layer 54. The third regions
58c are sized similarly to the second regions 58b and are formed
with a similar convergent profile.
[0026] The second bore layer 60 includes a larger region 64 that
surrounds the third regions 58c and is subjected to the
electromagnetic radiation so as to undergo polymeric cross-linking
and become insoluble in developing solutions. The region 64, which
is not subsequently removed, becomes the raised portion 38 of the
fluidic layer assembly 24. The region 64 typically extends the
entire length of the second bore layer 60 and has a width that is
substantially equal to the desired width of the raised portion,
which could be 150 microns, for example, or could be as large as
half the die or more. The portions of the second bore layer 60
lying outside of the region 64 are additional areas to be removed
and are thus not exposed to electromagnetic radiation.
[0027] After the first and second bore layers 54 and 60 have been
exposed, they are jointly developed (again using any suitable
developing technique), to remove the unexposed, soluble bore layer
material and leave the exposed, insoluble material, as shown in
FIG. 8. This results in the fluidic layer assembly 24 collectively
made up by the chamber layer 46, the first bore layer 54, and the
second bore layer 60 wherein the remaining portion of the first
bore layer 54 makes up the base portion 40 and the remaining
portion of the second bore layer 60 defines the raised portion 38.
The raised portion 38 is thus formed on the second side 36, with
the low drop weight nozzles 16a being formed in the base portion 40
and the high drop weight nozzles 16b being formed in the raised
portion 38. In addition, the fill material 52 filling the void 50
in the chamber layer 46 is also removed, leaving a substantially
closed space defining the firing chambers 28 and the feed channels
30 that are in fluid communication with the nozzles 16a, 16b. The
ink feed hole 26 is then formed in the substrate 20 using any
suitable technique, including wet etching, dry etching, deep
reactive ion etching (DRIE), laser machining, and the like.
[0028] Turning now to FIGS. 9-11, another process for fabricating
an inkjet printhead 12 is described. The initial steps for
preparing the substrate 20, the thin film stack 22, and the chamber
layer 46 (including the void 50 and the fill material 52) are
essentially the same as described above and, as such, are not
repeated here. As in the first embodiment, the layers comprising
the fluidic layer assembly 24 can be formed of any suitable
photoimagable materials. By way of example, the layers in this
embodiment will also be described as comprising a negative
photoresist material, although positive photoresists could
alternatively be used.
[0029] Once the chamber layer 46 has been applied and processed, a
layer of photoresist material is applied to a desired depth on the
upper surface of the chamber layer 46 to provide a first bore layer
54, as shown in FIG. 9. The fill material 52 again keeps first bore
layer material out of the void 50 in the chamber layer 46. The
first bore layer 54 is possibly, although not necessarily, made of
the same material as the chamber layer 46.
[0030] The first bore layer 54 is then imaged by exposing selected
portions to electromagnetic radiation through a fourth mask 66,
which masks certain areas of the first bore layer 54 and does not
mask the remaining areas. The areas that are not masked, and are
thus exposed to radiation, undergo polymeric cross-linking and
become insoluble in developing solutions. In this exposure, the
entire left side (as seen in FIG. 9) of the first bore layer 54 is
exposed except for a first series of relatively small regions of
soluble material 58a (only one shown in FIG. 9) that will become
the low drop weight nozzles 16a. In the illustrated embodiment, the
first regions 58a are aligned with corresponding fluid ejectors 32
and are formed using a suitable focus offset to provide convergent
profiles. The right side of the first bore layer 54 is not exposed
at this time.
[0031] Referring to FIG. 10, the first bore layer 54 is further
imaged by exposing selected portions to electromagnetic radiation
through a fifth mask 68, which masks certain other areas of the
first bore layer 54 and does not mask the remaining areas. In this
exposure, the entire right side of the first bore layer 54 that was
not previously exposed is exposed except for a second series of
relatively small regions of soluble material 58b (only one shown in
FIG. 10) that will become the high drop weight nozzles 16b. In the
illustrated embodiment, the second regions 58b are aligned with
corresponding fluid ejectors 32 and are formed with a low focus
offset (e.g., about 4 microns or less) to create a divergent
profile. This will prevent any mixing of the fill material 52 and
the unexposed first bore layer material.
[0032] The fourth and fifth masks 66 and 68 can be patterned such
that the first regions 58a will be smaller than the second regions
58b, so that the high drop weight nozzles 16b will have larger
cross-sectional areas than the low drop weight nozzles 16a. For
example, the first regions 58a can be sized to be 13 microns in
diameter, while the second regions 58b can be sized to be 20
microns in diameter. The first bore layer 54 is typically not
developed at this point in the process.
[0033] Referring to FIG. 11, another layer of photoresist material
is applied to a desired depth on top of the first bore layer 54 to
provide a second bore layer 60. The second bore layer 60 is
possibly, although not necessarily, made of the same material as
the chamber layer 46 and/or the first bore layer 54. The second
bore layer 60 is then imaged by exposing selected portions to
electromagnetic radiation through a sixth mask 70, which masks the
areas of the second bore layer 60 that are to be removed and does
not mask the areas that are to remain. Selected portions of the
first bore layer 54 are also cross-linked by this exposure, thus
reducing the amount of soluble material in the second regions 58b.
The areas of the second bore layer 60 that are to be removed
include a series of third regions of soluble material 58c, wherein
each third region 58c is aligned over a corresponding one of the
second regions 58b in the first bore layer 54. The third regions
58c are formed using a focus offset that provides a convergent
profile.
[0034] The second bore layer 60 includes a larger region 64 that
surrounds the third regions 58c and is subjected to the
electromagnetic radiation so as to undergo polymeric cross-linking
and become insoluble in developing solutions. The region 64, which
is not subsequently removed, becomes the raised portion 38 of the
fluidic layer assembly 24. The region 64 typically extends the
entire length of the second bore layer 60 and has a width that is
substantially equal to the desired width of the raised portion,
which could be 150 microns for example. The portions of the second
bore layer 60 lying outside of the region 64 are additional areas
to be removed and are thus not exposed to electromagnetic
radiation.
[0035] After the first and second bore layers 54 and 60 have been
exposed, they are jointly developed (again using any suitable
developing technique), to remove the unexposed, soluble bore layer
material and leave the exposed, insoluble material. This results in
the fluidic layer assembly 24 (collectively made up by the chamber
layer 46, the first bore layer 54, and the second bore layer 60)
having the raised portion 38 formed on the second side 36, with the
low drop weight nozzles 16a formed in the base portion 40 and the
high drop weight nozzles 16b formed in the raised portion 38. In
addition, the fill material 52 filling the void 50 in the chamber
layer 46 is also removed, leaving a substantially closed space
defining the firing chambers 28 and the feed channels 30 that are
in fluid communication with the nozzles 16a, 16b. The ink feed hole
26 is then formed in the substrate 20 using any suitable technique,
including wet etching, dry etching, deep reactive ion etching
(DRIE), laser machining, and the like.
[0036] Turning now to FIGS. 12 and 13, yet another process for
fabricating an inkjet printhead 12 is described. Again, the initial
steps for preparing the substrate 20, the thin film stack 22, and
the chamber layer 46 (including the void 50 and the fill material
52) are essentially the same as described above and, as such, are
not repeated here. As in the first two described embodiments, the
layers comprising the fluidic layer assembly 24 can be formed of
any suitable photoimagable materials. By way of example, the layers
in this embodiment will also be described as comprising a negative
photoresist material, although positive photoresists could
alternatively be used.
[0037] Once the chamber layer 46 has been applied and processed, a
layer of photoresist material is applied to a desired depth on the
upper surface of the chamber layer 46 to provide a first bore layer
54, as shown in FIG. 12. The fill material 52 again keeps first
bore layer material out of the void 50 in the chamber layer 46. The
first bore layer 54 is possibly, although not necessarily, made of
the same material as the chamber layer 46.
[0038] The first bore layer 54 is then imaged by exposing selected
portions to electromagnetic radiation through a seventh mask 72,
which masks certain areas of the first bore layer 54 and does not
mask the remaining areas. The areas that are not masked, and are
thus exposed to radiation, undergo polymeric cross-linking and
become insoluble in developing solutions. In this exposure, the
entire left side of the first bore layer 54 (as seen in FIG. 12) is
exposed except for a first series of relatively small regions of
soluble material 58a (only one shown in FIG. 12) that will become
the low drop weight nozzles 16a. In the illustrated embodiment, the
first regions 58a are aligned with corresponding fluid ejectors 32.
The right side of the first bore layer 54 is not exposed at this
time.
[0039] Referring to FIG. 13, another layer of photoresist material
is applied to a desired depth on top of the first bore layer 54
(before developing the first bore layer 54) to provide a second
bore layer 60. The second bore layer 60 is possibly, although not
necessarily, made of the same material as the chamber layer 46
and/or the first bore layer 54. The second bore layer 60 is then
imaged by exposing selected portions to electromagnetic radiation
through an eighth mask 74, which masks the areas of the second bore
layer 60 that are to be subsequently removed and does not mask the
areas that are to remain. This exposure step also exposes certain
areas in the portion on the right side of the first bore layer 54
that were not previously exposed. The areas of the first and second
bore layers 54 and 60 that are to be removed include a second
series of relatively small regions of soluble material 58b in the
first bore layer 54 and a third series of relatively small regions
of soluble material 58c in the second bore layer 60 (only one of
each shown in FIG. 13) that will become the high drop weight
nozzles 16b. Accordingly, between the two exposures, the entire
first bore layer 54, except for the first and second regions 58a
and 58b, is exposed to radiation. In the illustrated embodiment,
the second and third regions 58b and 58c are aligned with each
other and with corresponding fluid ejectors 32. The seventh and
eighth masks 72 and 74 can be patterned such that the first regions
58a will be smaller than the second and third regions 58b and 58c,
so that the high drop weight nozzles 16b will have larger
cross-sectional areas than the low drop weight nozzles 16a. For
example, the first regions 58a can be sized to be 13 microns in
diameter, while the second and third regions 58b and 58c can be
sized to be 20 microns in diameter.
[0040] The second bore layer 60 includes a larger region 64 that
surrounds the second regions 58b and is subjected to the
electromagnetic radiation so as to undergo polymeric cross-linking
and become insoluble in developing solutions. The region 64, which
is not subsequently removed, becomes the raised portion 38 of the
fluidic layer assembly 24. The region 64 typically extends the
entire length of the second bore layer 60 and has a width that is
substantially equal to the desired width of the raised portion,
which could be 150 microns for example. The region 64 is preferably
large enough to overlap (as shown in FIG. 13) the portion of the
first bore layer 54 that was exposed during the first exposure
step. The remaining portions of the second bore layer 60 are
additional areas to be removed and are thus not exposed to
electromagnetic radiation.
[0041] After the first and second bore layers 54 and 60 have been
exposed, they are jointly developed (again using any suitable
developing technique), to remove the unexposed, soluble bore layer
material and leave the exposed, insoluble material. This results in
the fluidic layer assembly 24 (collectively made up by the chamber
layer 46, the first bore layer 54, and the second bore layer 60)
having the raised portion 38 formed on the second side 36, with the
low drop weight nozzles 16a formed in the base portion 40 and the
high drop weight nozzles 16b formed in the raised portion 38. In
addition, the fill material 52 filling the void 50 in the chamber
layer 46 is also removed, leaving a substantially closed space
defining the firing chambers 28 and the feed channels 30 that are
in fluid communication with the nozzles 16a, 16b. The ink feed hole
26 is then formed in the substrate 20 using any suitable technique,
including wet etching, dry etching, deep reactive ion etching
(DRIE), laser machining, and the like.
[0042] While specific embodiments of the present invention have
been described, it should be noted that various modifications
thereto could be made without departing from the spirit and scope
of the invention as defined in the appended claims.
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